“Yes, it could be triggered if such a war started by an attack by China on American forces in the Pacific”
Bingo.
I disagree with you on calling it spin. I believe Downer meant what he said and was appeasing the Chinese communists and was backing away from the alliance specifically vis-a-vis Taiwan independence.
Downer was not a maverick in this in the foreign affairs community with many arguing against US support for Taiwan - the Taiwan was provoking it viewpoint.
He was being specifically asked if Australia was obliged to go to war under ANZUS if the US went to war against China because Taiwan was attacked.
That was the specific question he was asked.
And in that context, he said no, ANZUS would not apply.
He was entirely accurate in saying so - because that would be a war triggered not by an attack on the US anywhere, but by an attack on Taiwan.